Radio frequency amplitude control device



L. G. FISCHER RADIO FREQUENCY AMPLITUDE CONTROL DEVICE F'lled Aug 23,1951 TIZANSM/TTEI? 5 2 TRANSMITTER Oct. 6, 1953 ullsllflllv PatentedOct. 6, 1953 ammomuseum1%; A

MPIlITUDEt-CDNTRDL VICE stem-Federal mmunieationgjzhaboratnries,

..;Jnc.,.:-Nutley, LNJam corporatiomoL-Delaware Applicationkugust23,195,1,SeriaLl'N6Lf2'43flB3 One "of the principal-objects ofthisin-vention (is-to provide meansforadjusting-the amplitude of aradiofrequencywave insuch a manner "as ito'maintain" a purely resistivenhaler-constant load on the transmitter.

1A riurther obj ect toprovide means "for-- a'ddustingunmodulatingthetamplitudeoi' :aninput radio frequency wave in such 'a'manner uhat .th'e output wave or 'waves"will always "be'in like "phasewith theinputwave.

A feature of-this'"invention'isthe simplicity of the "amplitude controldevice. The device, for examp'1e,r'may"employ conductors "and a pair .ofgivenloads connected toi'orm a closed loop 'inwhi'chithe given loads are"substantially a half wavelength gapart. Theinput to the lojorris-"bymeansof a pair o'fmovable"couplingelements. "The output is taken offatthe given "loads either "as the sine "or cosine of the "angleof-rotationdf 'the coupling elements, or both simultaneously.

"The amplitudepftheoutputwaves*vary "'with the positioning of thecoupling elements alongthe "perimeter of the loop. The -twooutput-"waves absorb the input "energy in a complementary 'mannerythusproviding a purely "resistive load on the transmitter without anyphaseifsliiftbeing "introduced.

Another feature -'oi *th'is' i-nvention isthe radio frequency amplitudemodulating capabilities of the device. Modulation is ohtained by':rotating coupling lemen ts within. :a circular "loop *wherein "theamplitude modulating function may" be expressed as directly xequal toi'the 's1ne" of' the r rotational angle. Useful outputsOOIItIOIIG'CIEiIlflJIH- =plitude" are obtainable.*For-example; if themodu'lation desired is we) ,"=then the rotational function f(o):rsine-=i x)i "The; above mentioned and other features "and objectsof "thisinvention "will becomemore *apparent byireference'fito the followingdescription 1 i'ssmschematic representation of-a dece according to theprhidiples of this-inven- *tion;

-Fig; 21s a "diagram or "the voltage vector relations I existing in thedevice of Fig. 1

Fig' 3 is a longitudinal sectional view of one embodiment for use as abalanced sinusoidal amplitude modulator;

Fig. 4- is a cross-sectional view taken. line 4-4 of Fig. 3; and

Fig. 5 is a view in side elevation of another embocliment'ioriuse as anamplitude adjustor.

Referring to Fig. 1, an amplitude control device l is shown coupled to atransmitter 2 through a balanced line 3. The device I comprises a loopcomposed ofconductors Hand 5, each substantially a halt wavelength longor multiple along the :tthereoi; 'J'oineflbyrgiven :l'oari resistors "6and fl sometimes; hereinafterireferred to as :intemal or dump loads. Twomovable coupling capacitive elements BHand'Qctransmit the :inputrto theloop. Tworshorteiiaoutput connectors -1Lil and 5.1 i, :each anuanterzoraan odd multiple TOffl a "quarter wavelength :long; $9318connected at-ithe resistive loads "-Giand 1. *mnvtaexzternalaload l2iswconnected to the ecentervofithe.Lshorted ends of these outputeoonrreotors 51120 rand :H.

i While :resisti-ve :loads 6 and 1 :may be "referred :tovasidump"r1o'ads,i theyzmay alsobe useful isl'oa'dsn- Insnn'eexample'vmereitis desired to feed :v iquadrazturezzmodulation woltagesto equal pairs of" antennas, :Tone phase can be "obtained from-pointsra; b as thmcosine of therotational angle-0 cofi'elements 8 and"9, while anoth'er voltage phase :obtained'trom moth sets 'of points 0,d and e; 'f

as; theiisin'e of the rotational angle.

fi fsince "coupling elements '8 and "9 are fed from a ba'lanced line 3*,they are 1130" "out of phase. If the ceupling' elementsare displacedmidway between the resistive-loads G and 1, the voltage apnearing at-point a irom'coupl ing element 8 will be *equal anti ol" thesame signto the voltage appearing at point b from coupling element 9. Thevolta'ges :at -cand it *due to coupling elements 8 and 9 are equal andopposite insignfilikewise, the voitages at eand are equal and opposite.for themidwaypositioning of elements '8 "and "9; no power will be fed-to the "external "load P2; but all ofthe power Will "be dissipated inresi'stive loads 6 and 1. "'Ifthe couplingelements .8 andWare-movedso""theyare directly opposite be divided between the two loads6, l on the one hand and, on the other hand, the external load I2. Theloads at 6, l, and I2 may all comprise useful loads, the output atpoints a and b being proportioned to cosine 0, and the output betweenand d on the one hand and e and f on the other hand being eachproportional to sine 0.

The loads of c, d and e, f are each equal to 220. and the load at a andb is equal to Z0.

Referring to Fig. 2, the voltage vector relatio existing in theamplitude control device of Fig. -l is shown as when the couplingelements are in an intermediate position, displaced from the resistors 6and l by an angle 9. The voltage drop across the internal loads are E6and E7. These voltages vary as the sine 0. The voltage drop across theexternal load Er. varies as cosine 0. The total load supplied by thetransmitter when each resistor has a resistance of twice the externalload Z0 is:

Hence the load on the transmitter is constant and not affected by theposition of the coupling elements.

An embodiment of the device shown schematically in Fig. 1 is illustratedas a balanced sinusoidal amplitude modulator in Figs. 3 and 4. The samereference characters are used for corresponding parts in the twoillustrations. A disc l3, made of insulating material support the twocoupling elements 8 and 9 and is caused to rotate within the circularloop by means of a motor I l. The coupling elements 8 and El areconnected to the input by means of a balanced line 3 through slip ringsl5, c and brushes l6, Ilia, the rings being conductively coupled to thecoupling elements 8 and 9, respectively. The quarter wavelength shortedoutput connectors l6 and II are connected across said resistors 6 and land are inclined from the periphery of the loop and are joined to outputconnectors l1, l8, respectively, at the center of their shorted ends.The loop and coupling elements are preferably contained in a housing I!)lined with insulation 20. If the coupling elements are rotated at aconstant angular velocity, the in ut wave is amplitude modulated withoutany phase shift. By replacing the motor M with a manual control, theunit may be used as an amplitude adjustor.

In the embodiment shown in Fig. 5 a manual control 2i is shown inassociation with a rectangular loop 22. The rectangular loop comprisestwo conductors 4a and 5a, each a half wavelength long joined by tworesistors 6a and la. Two racks 23 and 24 of insulating material, such asMicarta, are shown carrying the two coupling elements 8a and 9aconnected to an input by means of a balanced line 3a. The racks arelaterally displaced, by means of the manual control 2| operativelyconnected to a pinion 25, equal distances from resistors 6a and 1a andin opposite directions. The output is taken from across said resistorsby means of quarter wavelength connectors Illa and I la as described inconnection with Fig. 1.

Many variations in the structure of the embodiments shown will occur tothose skilled in the art, for example, replacing the capacitive couplingelements 8 and 9 with sliding contacts is believed preferable in someapplications, also the conductors 4 and 5 may be of any desiredcrosssectional shape or loop arrangement. Further, where the conductors4 and 5 are said in the claims to be equal substantially to a halfwavelength each, such expression is intended to cover multiples of ahalf wavelength as well. Also, where the shorted stubs l0 and H arereferred to as equal to substantially a quarter wavelength, the same isintended to include odd multiples of a quarter wavelength. It is to beunderstood, therefore, that the particular embodiments disclosed in thisapplication are to be regarded as illustrative only and not as alimitation to the invention as set forth in the objects thereof and theaccompanyin claims.

I claim:

1. A radio frequency amplitude control device comprising twosubstantially half wavelength conductors and a pair of given loadscoupling said conductors in series to form a loop, a third load, a pairof output connectors each equal to substantially a quarter wavelength,each of said connectors being coupled to said loop at the terminals ofsaid given loads, means to couple said third load to said connectors, apair of input coupling elements disposed in coupling relation to saidloop at points spaced apart along said loop by substantially a halfwavelength, and means for changing the coupling position of saidelements with respect to said loop.

2. A device according to claim 1, wherein said connectors comprise twoquarter wavelength shorted stubs, the legs of one stub being coupled tothe terminals of one of said given loads and the legs of the other stubbeing coupled to the terminals of the other of said given loads.

3. A device according to claim 1, wherein the perimeter of said loop isequal to one wavelength and said given loads are separated by loopportions, each equal substantially to a half wavelength.

4. A device according to claim 1, wherein said loop is of circularconfiguration and said given loads are located at diametrically opposedpoints in said loop.

5. A device according to claim 4, wherein the said means for changingthe coupling position of said elements includes a rotor supporting saidcoupling elements for rotation.

6. A device according to claim 1, wherein said loop is of rectangularconfiguration and said given loads are coupled in opposite sides of saidrectangle.

7. A device according to claim 6, wherein said means for changing thecoupling position of the coupling elements includes means for moving thesaid coupling elements equal distances in opposite directions.

8.. A device according to claim '7, wherein said last-mentioned meansincludes a pair of racks and a. pinion in mesh therewith, each rackcarrying one of said coupling elements.

9. A radio frequency amplitude modulating device comprising a circularloop composed of two conductors each substantially a half wavelengthlong and two given loads joining said conductors, two coupling elements,a disc of insulating material on which said coupling elements aremounted at diametrically opposite points and disposed in couplingrelation to said loop, a transmitter, means to couple said transmitterto said disc, means to rotate said coupling elements in accordance withthe modulations desired, two substantially quarter wavelength shortedstubs, each connected to the terminals of one of said given loads,output connectors connected to said shorted stubs at their shorted ends,a third load connected to said output connectors, the resistance of saidthird load being substantially equal to one half the resistance of eachof the said given loads.

,whereby the output wave is modulated in accordance with the rotationalangular velocity of said coupling elements.

10. A device according to claim 9, wherein said means to rotate saidcoupling elements includes a constant speed motor operatively connectedto said disc whereby said coupling elements will be rotated at constantangular velocity and the output wave will be sinusoidally modulated.

11. A device according to claim 9, wherein said means to connect thetransmitter to said coupling elements includes a balanced line, brushes,and slip rings.

12. A radio frequency amplitude control device comprising a loop circuithaving in series a first conductor, a first load, a second conductor,and a second load, each 01 said conductors being equal substantially toone-half wavelength, a source of input energy, means to capacitivelycouple said energy to said loop circuit at points spaced apart bysubstantially a halt wavelength, means for varying the position of said.capacitive coupling with respect to said first and second loads, a firstand second output connector each substantially a multiple of a quarterwavelength coupled respectively to the terminals 01' said first andsecond loads, a third load, and means to couple said third load to saidfirst and second output connectors.

13. A radio frequency amplitude adjusting device comprising arectangular loop composed of two conductors and two given loads, saidloads coupling said conductors in series to form said rectangular loop,said conductors being substantially a half wavelength long, a pair ofinput coupling elements disposed in coupling relation to said loop atpoints spaced apart along said loop by substantially a half wavelength,means for moving said coupling elements equal distances in oppositedirection along opposite sides oi. said rectangular loop, two quarterwavelength shorted output connectors each coupled to the terminals ofone of said two given loads, and a third load connected to the shortedends o1 said output connectors, said third load having a resistanceequal substantially to one half the resistance of each of said givenloads.

14. A device according to claim 13, wherein the means for moving saidcoupling elements comprises a rack and pinion mechanism and means forcontrolling said mechanism.

LAURIN G. FISCHER.

References Cited in the tile 01' this patent UNITED STATES PATENTSNumber Name Date 2,368,693 Watts, Jr. Feb. 6, 1945 2,451,201 Clark, Jr.Oct. 12, 1948 2,492,138 Earp Dec. 27, 1949

